Update 0216.组合总和III.md

感觉这种解法更符合卡哥视频的讲解。

problems/0216.组合总和III.md

@@ -397,24 +397,31 @@ func backTree(n,k,startIndex int,track *[]int,result *[][]int){
  * @return {number[][]}
  */
 var combinationSum3 = function(k, n) {
-    const backtrack = (start) => {
-        const l = path.length;
-        if (l === k) {
-            const sum = path.reduce((a, b) => a + b);
-            if (sum === n) {
-                res.push([...path]);
-            }
-            return;
+    let res = [];
+    let path = [];
+    let sum = 0;
+    const dfs = (path,index) => {
+        // 剪枝操作
+        if (sum > n){
+            return 
         }
-        for (let i = start; i <= 9 - (k - l) + 1; i++) {
+        if (path.length == k) {
+            if(sum == n){
+                res.push([...path]);
+                return 
+            }
+        }
+        for (let i = index; i <= 9 - (k-path.length) + 1;i++) {
             path.push(i);
-            backtrack(i + 1);
-            path.pop();
+            sum = sum + i;
+            index += 1;
+            dfs(path,index);
+            sum -= i
+            path.pop()
         }
     }
-    let res = [], path = [];
-    backtrack(1);
-    return res;
+    dfs(path,1);
+    return res
 };
 ```